Gaddafi's sons have fled their stronghold of Bani Walid, scuppering negotiations for its surrender and leaving behind a squad of troops with orders to defend it using the residents as human shields, according to rebel forces.

Gaddafi's sons have fled their stronghold of Bani Walid, scuppering negotiations for its surrender and leaving behind a squad of troops with orders to defend it using the residents as human shields, according to rebel forces.

Saif al-Islam and Mutassim Gaddafi were said to have been in the town as recently as last week. The town is one of only three major Libyan centres still holding out for the former leader.

Rebel military leaders said residents had told them that the two had fled, leaving behind a detachment of up to 100 loyalist troops and local allies who had taken up positions in private houses in anticipation of a rebel attack.

"The main Gaddafi brigade left with Saif al-Islam," said Abdullah Kenshil, the chief negotiator for the rebels. "We think there are 70 troops left there in the town, but there are other people with them." He added that residents were being prevented from fleeing.

Col Abdulrazzaq al-Nadouri, the deputy commander of rebel forces based in the town of Tarhouna, about 50 miles to the north, added: "Some of them (Gaddafi forces) are hiding in local families which they are using as human shields. We're afraid for the families."

Rebel troops on the ground have been threatening to attack Bani Walid, the headquarters of Libya's biggest tribe, the Warfalla, but the National Transitional Council is afraid of further divisions and bloodshed. Many Warfalla opposed Gaddafi, particularly after scores were executed following a coup attempt in the early 1990s, and are resentful some Warfalla leaders continued to support him.

The council has been trying to negotiate a peaceful end to the stand-off with Moussa Ibrahim, the chief spokesman for the Gaddafi regime. Mr Ibrahim was said to have demanded face-to-face talks and that the rebels disarm first.

Rebel spokesmen in Benghazi fear the stand-off at Bani Walid was deliberately orchestrated to give the family time to escape to the porous desert borders.

The rebels have extended to Saturday a deadline for the surrender of Sirte and other loyalist areas, though some rebel officials have said they could attack Bani Walid sooner because it has so many prominent loyalists.